A layer 3 network is the third layer in an Open Systems Interconnection (OSI) model. A forwarding device, such as a router or a network switch, applied to a layer 3 network forwards a data packet according to a routing table. The routing table is established according to an Internet Protocol (IP) address.
In a layer 3 network, when a network topology changes, if a routing table is not updated, routing entries in routing tables may contradict each other, resulting in a routing loop. Because of the routing loop, a packet is cyclically transmitted among several fixed routers in the network and cannot reach a destination host.